Monthly Archives: December 2012

Table for one, please

If you ponder the question of why female spiders frequently eat their mates (frequently, not always) you sometimes arrive at the question, “Why not?” They’re usually solitary creatures, those spiders, with nothing to say to each other, no shared hobbies or interests, and they refuse to stay together for the children. In fact, sometimes they eat the children, but that’s another story.

A spider man that tumbles into a female spider’s embrace is likely to be smaller than she (easier to overpower), eager to get perilously close to her fangs, and a nice packet of nutrition for the future mother to be. All of which makes great sense … for her. But is a fella more than just a snack?

It turns out to be rather more mysterious. And I like mysterious spiders. A new study of wolf spiders in China (Pardosa pseudoannulata) tried to tease out the matter of who eats whom, how often, and under what circumstances. Was she just hungry? Was the luckless suitor too inexperienced? The scientists paired off dozens of spiders, both virgin and experienced, and tabulated a number of different ways the blind dates turned out.

I am Pardosa, hear me roar. Where’s that bum that promised me dinner?

Ten percent of the virgin females ate their dates without even mating. Twenty-eight percent ate them right after mating. Both hungry gals (as opposed to recently fed) and those who had previously mated or laid egg sacs were more aggressive than the debutantes. The bigger the size differential (dimorphism) the more likely the male would become a meal. Nobody got eaten during the act itself. All very gothic and kind of comprehensible.

At this point, do the numbers … most of the males therefore got away. That’s interesting in its own right. More interesting is what follows.

There turned out to be a clear result from all these enchanted encounters: the females that had noshed on a male after mating had the same number of offspring as those who hadn’t (in other words, fecundity was unaffected) but those offspring survived better. They were vigorous spiderlings who looked to have a better shot at making it to adulthood. That rings the Darwinian gong in the clearest possible way: cannibalizing a mate gives your progeny, your genes, a leg up—eight legs up—in the grand contest with no finish line.

Of course not. Spiders and salmon don’t want anything of the kind. Nor do they set up IRAs and college accounts for their offspring. If daddy long-legs’ death contributes to the hardiness of baby long-legs, than it’s going to happen. You don’t need God or Dr. Spock to coax it along. We packets of DNA do things like that because our ancestors, having done them, thrust their genes into the future, our present. And we will continue doing the things that work, because they have worked.

A remaining question, in the Mystery of the Dined-On Daddy, is what exactly his little carcass does for his mate and her egg sac. Nobody knows what the secret ingredient is, if there is one. Maybe the least romantic females were already equipped to make better offspring, so the male just managed to get a bad spin on the Wheel of Life even as his genes hit the jackpot.

The artists among the Cyclosa community — those small orb-weaving spiders, known for decorating their webs with trash — are getting better. At least in one corner of Peruvian rainforest, where someone with an ecotourism company spotted this tiny sculptor having an exhibition at roughly eye level. Now, the trash-line spiders have long been observed cluttering up their homes purposefully. It’s not that they’re lousy housekeepers. It seems that if you compile a, well, pile of dead bugs and other debris you might attract more predators, but those predators will have a lesser chance of picking you out among the junk. Smart, those spiders. What you call a strategy of pre-emption.

But this photo by Phil Torres of Rainforest Expeditions is yet more marvelous. Walking among the brush, Torres spotted what he thought was a live spider wiggling and twisting in a web. But it looked off … flaky and dried-out. As well it should, since it was made of bits of leaf and bug body parts. The actual spider was right nearby, tinier than its mummy, and it apparently was giving the web a twang now and then to make the scarecrow move about realistically. Torres found multiple members of this still-unidentified species not far away.

As much as I love to anthropomorphize, I know this small creature wasn’t thinking of Day of the Dead flair as it did its work. In fact, for all the amusement and fascination this image is sparking on the internet, it’s not clear that there was anything deliberate in the spider-shaped accretion. The silk lines do happen to converge there, spiders like to sit where the lines meet, and it’s possible the junk collection merely overflowed. Still, other Cyclosa research has shown that those who tend to make decoys usually build them about the same size as their bodies, which is interesting. If these spiders have an instinct for making scarecrows (scarespiders?), the legs are a natural next step. (Other photos on the site show effigies with eight legs, a realistic touch that really gives you pause). I like the contrast between the big, spooky decoy and the brisk, tiny spider doing the work.

One giant leap for spiderkind – a lot of leaps, actually

The universe’s most well-traveled spider, a Phidippus johnsoni with the grand name of Nefertiti, died recently in what was supposed to be her quiet retirement home. Reporters made much of how this chunky, red-and-black jumper not only thrived in her 100 days aboard the International Space Station but withstood the rigors of launch, re-entry, and being shuttled about the country with apparent good grace. Nefertiti seems to have reached the end of her brief natural lifespan in the warm confines of an exhibit at the Smithsonian’s National Museum of Natural History.

Spiders have the right stuff, forgive me trotting out that phrase. They’re focused, efficient, and as taciturn as any Neil Armstrong. This particular arachnaut, a regular Sally Ride, had a simple mission that she performed with grace and energy: catching flies. And the wondrous thing: she did it in zero gravity, an environment no earthly spider could be expected to grasp. Think of those millions of years of earthbound instincts, honed to an unimagineable degree … and yet this jumping spider was all feh, I can do this—I’ll just adjust the trajectory here and the thrust there, disregard millennia of sensory input, and boom: bug soup.

What next! Spiders from Mars? Oh. Carry on then, Ziggy.

I don’t think any old spider could have done it. Jumping spiders are the brains of the outfit. Equipped with sophisticated, unblinking, networked cameras around their little heads, they see and hunt famously well. They’ve been observed sneaking up on prey that they can’t even see, calculating how to creep up under cover and burst out at just the right instant. It would be like you stalking a pizza delivery guy walking along on the other side of a tall fence, figuring out when he’s going to stop and tie his shoe or check his text messages, pursuing him around the corner, and then out you pop through a loose board and snatch his pie. Yep, it takes thought.

Nefertiti got her ticket to ride thanks to an 18-year-old Egyptian named Amr Mohamed, who won the YouTube Spacelab contest with his idea for a jumping-spider experiment. (There was a second arachnaut, a zebra-striped Salticus scenicus named Cleopatra, but alas, she died in orbit.) Once aloft, astronaut Suni Williams took the spiders under her wing and blogged about them. She remarked about Nefertiti: “She is sort of scary. I am so glad I am not a fruit fly. I opened up the habitat and actually saw her running around at full speed looking for something to eat. It was difficult to even get a steady picture.”

What, no Tang? Nefertiti is hungry, and she’s looking at you.

Watch her do it. It’s funny how earthlike it looks. She does that classic Salticid prowl, but I think she’s hanging on to the surface a bit more consciously, as astronauts do. Can’t see it, but surely she’s letting out a silk dragline before the leap to reel herself back in if she misses. But jumping spiders always do that on earth, too.

Nefertiti was not the first spider in space. Experiments involving zero-G web building by spiders also took place aboard Skylab (that’s old-school space program, kiddies), on the space station twice before, and on the shuttle Columbia. Australian high-school students designed Columbia’s science module to see whether eight garden-variety orb spiders could do their weaving and hunting jobs in space. Those spiders perished when Columbia was destroyed during re-entry in 2003.

Until recently, a brave little website by the Glen Waverley Secondary College devoted to that aborted spider experiment was still archived on the web, drifting forlornly through cyberspace. The tab labeled “Results” was blank.

But there’s more to that story, and not really about spiders but about science and humans. Most of the spider data was lost along with the shuttle and its crew, but spacecraft did fly again. The teenagers who planned that experiment with such care resolved to let their work stand as homage to the people who venture into space. There will be other experiments, schoolchildren will dream them up, and other lives long and short will be entwined into the struggle to find Big Picture answers in the warm earth and the cold silence of space.

In 2011 two golden orb-weaving spiders preceded Nefertiti on the International Space Station, delivered via shuttle Endeavour in its last flight, and put in more than two months in another web-building experiment. Only one survived the return trip, and it obliquely offered aspiring scientists and teachers a lesson in humility.

Details matter in science and spaceflight, often to a poignant degree. The students, amid their extremely detailed preparations, had named this arachnaut Gladys. Back on earth, she was determined to be a he.